Laminated transformer core having butt joints staggered along a straight line



United States Patent C) 3,189,860 LAMINATEI) TRANSFORMER CORE HAVING BUTT .IOINTS STAGGERED ALONG A STRAIGHT LINE Clarence G. Duenlre, St. Louis, Mo., assigner to Core Manufacturing Company, Washington, Mo., .a `corporation of Missouri Filed Sept. 5, 1963, Ser. No. 306,959 3 Claims. (Cl. 336-217) The present invention relates to transformer core windings, and is a continuation-in-part of application Serial No. 826,038 tiled July 9, 1959, now abandoned.

A primary object of the invention is to provide a transformer core having windings arranged to greatly reduce so as to virtually eliminate the noisy rattling of the joints of a core winding.

It is conventional practice to form a transformer core of a plurality of strip metal windings, with the joints of the windings being located on a leg of the core. These joints may be in the form of lapped joints or butt joints, and they may or may not be staggered. It is also weil known that the magnetic flux will seek the easiest path of travel, and, since the reluctance of air is greater than that of the metal used for transformer cores, the ux will by-pass the air gaps at the joints if an alternative path is provided. For this reason, joints are frequently staggered so that the flux traveling along one lamination can jump to the adjacent lamination at the air gap rather than bridge the air gap itself. This sudden change in direction of the tlux at the joints has heretofore produced a rattling of the joints with an accompanying high level of vibration noise.

The primary object of the present invention, which is to reduce so as to virtually eliminate this vibration noise is accomplished by providing spaced locking laminations each having its joint offset 90 or thereabout from the other joints in the core. Because the joint of these loching laminations are oiset from the other, or locked joints, each oitset lamination provides a continuous strip of metal at either side of the plurality of joints solas to hold those joints against noisy vibration. These locking laminations may be spaced apart by as many as twenty laminations, although the number of laminations between them can be varied as desired.

Another object of the present invention is to provide a means for locking core joints against rattling, which means does not detract from the iiux charactistics of the core. By offsetting the locking laminations so that their joints are located on a diierent leg from the joints of the locked down laminations, the linx which moves to an ad jacent lamination can readily travel through the locking lamination at each side of the locked in laminations. Therefore, if the offset laminations have any elect on the ux whatsoever, it is to provide extreme limits of travel of the flux whereby the linx will remain very near to its original path. In other words, there being no joints of the locking laminations near the locked in joints, the iiux can travel through the locking laminations without having to bridge an air gap in the vicinity of the other laminations. Obviously, with the many laminations located near the joints of the locking laminations, there is an easy path for the flux to bypass the air gap of the locking joints.

Still another object of the present invention is to provide a method of winding a transformer core which greatly reduces the stresses applied to the laminations after annealing. This method incorporates the step of cutting the individual laminations before annealing, so that cutting stresses are not permanently set up in the metal, but are eliminated by the annealing process after cutting.

Further objects and advantages of the invention will become apparent from a more detailed description to follow.

In the drawings:

FIGURE l is a schematic side elevation of a roll of metal strip partially unrolled in preparation tor cutting;

FIGURE 2 is a schematic View of a plurality of cut laminations;

FIGURE 3 is an elevational view of one embodiment of the core as wound upon an arbor;

FIGURE 4 is a partial enlarged View of a portion of the core of FIGURE 3;

FIGURE 5 is a View partially in section showing the core of FIGURE 3 incorporated into a modified shell type transformer having one coil and two core loops;

FIGURE 6 is a modified form of the invention showing a modied core on an arbor; and

FIGURE 7 is a view partially in section showing the core of FIGURE 6 incorporated into a core type transformer having two coil loops and one core.

The core arrangement is shown in FIGURE 3. Although the core in that figure is Wound upon an arbor, the same relative relationship of the laminations holds for the core as wound about the ltwo coils for the construction of a transformer, as illustrated in FIGURE 5.

Referring to FIGURE 3, the core lil is shown as comprising two groups of laminations 11 and 12. 'I'hese groups 11 and 12 may have identical numbers of laminations, or they may be different; in that respect. Group 11 is illustrated as comprising a plurality of single turn concentric laminations 13. Each lamination is cut to such a length that it will make one turn about the arbor and about the next innermost lamination, so that the ends 14 and 15 of each lamination abut one another. The ends 14 and 15 meet in a butt joint 16.

The joints 16 of each group 11 and 12 are offset some what, so as to provide a path around each air gap at the various joints 16.

There is an innermost lamination 20, also comprising a single turn. The lamination Ztl has ends 21 and 22 meeting in a butt joint 23. The butt joint 23 is oiset from the joint 16 by a quarter turn of the core.

The groups 11 and 12 are separated by another lamination 24, the joint 25 of which is also otiset 90 from the joint 16.

Finally, the outermost lamination 26 has a butt joint 27 which is odset from the joint 16 by a quarter turn.

The modiiied form of the core, as illustrated in FIG- URE 6, is formed similarly to that core of FIGURE 3, and the corresponding numbers are given primes for convenience of comparison. Thus the modication of FIG- URE 6 comprises a core 19' having two lamination groups 11 and 12', each comprising a plurality of con'4 centric laminations 13 having oltset butt joints 16. An innermost lamination 20 has ends 21 and 22' meeting at a butt joint 23. Another lamination 24' separating the groups 11 and 12 has an oiset joint 25. An outermost lamination 26 has its joint 27 also located on another leg.

The method of forming the core will now be described. As illustrated in FIGURE l, a roll 36 of sheet metal is partially unwound providing a strip which may be cut to a predetermined length. rl`he innermost lamination 20 is cut to that length which will make exactly one complete turn about an arbor 31. That lamination 20 is then wrapped about the arbor 31 with its ends 21 and 22 located as illustrated in FIGURE 3, so that its joint 23 will reside upon a predetermined leg of the core 10. The next succeeding lamination 13 is cut to such a length that it will make a single turn about the innermost lamination 20. That length may either be prealeaseo determined mathematically and measured, or the strip from the roll 3l) may be wrapped about the innermost llamination 2) and thereafter the cut made so that the ends 14 and 15 will meet at a butt joint 1o. The lamination 13 is wrapped about the first lamination Ztl' with its joint 1'5 located on a dilferent leg from the joint 23, that leg being an adjacent one as illustrated in FlGURE 3.

Succeeding laminations 13 are cut to length and wrapped upon the arbor 3-1 with their joints arranged in staggered fashion as illustrated. When the desired number of laminations 13 have been wrapped upon the arbor, a lamination 24 is cut to length so as to make a complete turn about the group 11 and its joint Z5 is located on the same leg of the core 1t) as the joint 23 of the innermost lamination 20.

The second group 12 is similarly cut and wrapped upon the arbor 31 with their joints 16 located on the same leg as the joints of the first group 11.

Finally, an outermost lamination 25 is cut and wound upon the arbor about the second group 12, and the joint 27 of the outermost lamination 26 is otset so as to be located upon the same leg as the joints 23 and 25.

It should be appreciated that as many groups 11 and 12 as desired may be wound upon the arbor, and that the groups 11 and 12 may have as many laminations as desired. lt is preferred that each group 11 and 12 may be separated by a lamination having its joint located on a different leg from the joints of the group laminations. The innermost and outermost laminations should similarly have their joints located on a different leg.

T he laminations are annealed in their form as wound upon the arbor 31. The annealing serves to relieve stresses after cuttinU and bending, which will have occurred prior thereto, and to provide a set for the windings thereby giving them a shape toward which they will tend to return if stretched from that shape.

After anealing, the core 19 is wrapped about one leg of a transtormer coil 32. Under one method of assembling the core on a coil transferring of the core 1i) from the arbor 31 to the coil 31?. can begin with the innermost lamination 2t?. That lamination 2li is removed from the arbor 31 and its ends 21 and 22 are separated so that the lamination 20 can pass over the coil 32. The ends 21 and Z2 are then released and, because of the annealing, the lamination 26 will tend to return to its shape as annealed upon the arbor 31. The joint Z3 of the innermost lamination 2@ will be located in the same relative position on the coil 32 as it was upon the arbor 31.

The next succeeding lamination 13, which is the iirst lamination of the group 11, is removed from the arbor 31 and its ends 14 and 15 are separated so that the lamination 13 will pass over the coil 32. The least amount of stress in the lamination will be incurred if the longest end 15 is first inserted into the coil winding 3:2 and then the shorter end 14 is allowed to snap into abutting contact with the end 15. The resulting joint 16 will be in the same relation to the joint 23 as it was upon the arbor, that is, located on an adjacent leg of the core 1t?.

Succeeding laminations 13 are similarly transferred from the arbor 31 to the coil 32. The lamination 24 which separates the groups 11 and 12 is transferred with its joint 25 being located on the same leg as the joint 23.

The second group 12 will be transferred beginning with the innermost lamination of that group, and the joints 16 of the second group 12v/ill be located on the same leg as the joint of the rst group 11. ln other words, the relationship of all joints upon the coil 32 Will be the same as they were upon the arbor 31. The outermost lamination 26 will have its joint 27 located on the same leg as the joint 23 and Z5.

Although the core can be assembled as aforesaid, an advantage of the construction of this core is that it can be assembled in groups of laminations. For example, consider the assembly of the lefthand core 1t? of FIG- URE 5. 1f the core is made available in the wound condition illustrated in FIGURE 3, it is first disassembled from the outside; thus the outer locking lamination 26 is removed by slight spreading of its ends that dei-ine the joint 2.7. Next all of the laminations of the group 12 are removed together. This is done by simultaneously ,separating or spreading the ends 14 and 15 of the lamination group 12 and removing the group 12 as a unit. Thereafter, the locking lamination 24 is removed by spreading its ends that define the joint 25. Then all of the laminations that define the group 11 are removed as a group by simultaneously spreading or separating the ends 14 and 15 that define the joints 15. Additional groups of laminations are similarly removed as are additional locking laminations that separate adjacent groups. Finally the inner locking lamination 2t) remains.

Assembly of the core 1Q about the coil 32 begins with the innermost locking lamination 29. The ends Z1 and 2 of this lamination are spread apart to receive the coil 32 between them. As the locking lamination is pulled through the Window of the coil 32, only those corners of the locking lamination that must be pulled through the window are distorted. 1n the preferred position of the joint 23 as illustrated in FIGURE 5, three of the corners of the rectangle defined by the locking lamination Ztl are not distorted at all and only the upper righthand corner is iiexed slightly as the locking lamination is pulled through the coil window into its position making a single turn about the coil.

With the locking lamination 2t? in place, the innermost group 11 of laminations is installed by simultaneously spreading the ends 14 and 15 apart far enough to receive the coil 32. As these ends are spread apart, there is virtually no bending at the corners of the rectangle delined by the lamination 13. To enable the ends 1li and 15 to be spread apart, the side or leg opposite the joints 16 (the leg on the left side of FGURE 3) ilexes enough to allow suficient spreading of the ends 1d and 15 of the laminations. lf the joints 16 are located on the leg of the core that is positioned in the window of the coil 32, virtually no bending occurs at the corners of the laminations 13.

The rest of the core assembly is similar to the foregoing. The locking lamination 24 is installed in place in the manner of the locking lamination 2l?, andthe remaining groups of laminations, like the group 12, are

installed in the same way as the group 11. Then the outer locking lamination 26 is installed in the way that the locking lamination 20 was installed.

This assembly of the core 10 is very easy and `can be done in a very short period of time. Yet the method of assembly that is made possible by the core construction is done without bending the corners of the lamination groups and With a minima-l bending of as few as one corner of each locking lamination. The `flexing of the leg of the laminations that permits separating the ends that define the joints of the laminations occurs within the elastic limit of the metal and therefore has little or no elect upon the shape of the core after assembly or upon the operating characteristics of the core as part of a transformer.

4The transformer illustrated in FIGURE 5 being a modilied shell type transformer, may have a second core 1t) wound about an opposite leg of the coil 32. That winding would be identical to the one already described. The method .of forming the transformer core 10 illustrated in FIGURE 6 is similar `to the method described for the core 1). The essential difference between the two `cores is that the core of FIGURE 6 is adapted for use in a core type transformer having one core loop 'and two coil loops.

Various changes and modifications may be made within the purview of this invention as will be readily apparent to those skilled in the art. Such changes and modification-s are within the scope and teaching of this invention as `defined by the claims appended thereto.

What is claimed is:

1. A transformer core comprising a plurality of groups of :concentric laminations defining a closed rectangular loop having four legs, each lamination making a single turn about the loop and having ends abutting one another to define a single butt joint, the butt joints of each group of laminations being located on a first leg of the core and being staggered along the leg in a substantially straight line, whereby when the ends of the laminations of a group are spread apar-t, each end is bounded on one side only by an adjacent lamination, at least one single turn locking lamination separating adjacent groups of laminations, each locking lamination having ends abutting one another to define a butt joint loe cated on a leg of the core different from the first leg, at least one innermost single turn locking lamination having ends abutting one another to -detine a butt joint located on .a leg different from the first leg, and at least one single turn outermost locking lamination having ends abutting one another to deiine ya butt joint located on a leg different from the first leg.

2. A transformer comprising a coil and at least one core, the coil having sides defining .a closed loop and an inner window space, the core comprising a plurality lof concentric metal strip laminations collectively defining a generally rectangular closed core loop Wrapped about a side .of the coil, one side of -t-he core loop being positioned in the window of the coil loop, each lamination making a single turn about the core loop and having its ends Iabutting each other to deline a butt joint, the laminations of the core including at least two distinct groups each comprising a plurality of lani-ina'tions the butt joints of which are successively staggered in a single direction along the side of the core loop positioned in the window of the coil loop, whereby each group of laminations can be assembled as a group with a minimum of bending of the laminations, at least one looking metal strip lamination surrounding the outermost lamination group, the locking lamination making a single turn about the cor-e loop land having its ends abutting each other to deline a 'butt join-t, the butt joint of the locking lamination being spaced around at least one corner of the rectangle defined by the cor-e loop from the joints of the lamination groups and therefore being 1ocated Ioutside the window of the coil, at least one locking metal strip lamination adjacent the inner sides of the innermost lamination group, the last named locking lamination making a single turn about the core loop and having its ends abu-tting each other to detine a butt joint, the last named butt joint being spaced around at least one corner of the cone loop from the joints of the lamination groups, and at least one locking lamination between adjacent groups of laminations, the last named locking lamination making a single turn about the core loop .and 'having its ends abutting each other to define a butt joint, the last named butt joint being spaced around at least one corner of the core loop from the joints of the laminat-ion groups.

3. A transformer core comprising a plurality of groups of concentric laminations defining a closed rectangular loop having four legs, each lamina-tion making a single turn about the loop and having ends yabutting one another to deiine a single butt joint, the butt joints on each group of laminations being located on a first leg of the core and being staggered along the line in a substantially straight line, whereby when the ends of the laminations of a group are lspread apart, each end is bounded on one side only by an adjacent lamination, at least one single turn locking lamination, the locking lamination hav-ing ends abutting one another to define a butt joint located on a leg of the cor-e ditierent from the first leg.

References Cited by the Examiner UNITED STATES PATENTS 2,523,071 9/50 Somerville 336--217 X 2,548,624 4/51 Sclater 3-36-213 X 2,927,366 3/60 'Link 336--213 X `2,973,494 2/61 Ellis 336-217 3,001,163 9/61 ,'Pfuntner et al 336213 X 3,025,483 3/63 :Treanor 336--217 3,107,415 10/63 Ellis 29-l65.58

FOREIGN PATENTS 106,986 6/ 17 Great Britain.

JOHN F. BURNS, Primary Examiner. 

3. A TRANSFORMER CORE COMPRISING A PLURALITY OF GROUPS OF CONCENTRIC LAMINATIONS DEFINING A CLOSED RECTANGULAR LOOP HAVING FOUR LEGS, EACH LAMINATION MAKING A SINGLE TURN ABOUT THE LOOP AND HAVING ENDS ABUTTING ONE ANOTHER TO DEFINE A SINGLE BUTT JOINT, THE JOINTS ON EACH GROUP OF LAMINATIONS BEING LOCATED ON A FIRST LEG OF THE CORE AND BEING STAGGERED ALONG THE LINE IN A SUBSTANTIALLY STRAIGHT LINE, WHEREBY WHEN THE ENDS OF THE LAMINATIONS OF A GROUP ARE SPREAD APART, EACH END IS BOUNDED ON ONE SIDE ONLY BY AN ADJACENT LAMINATION, AT LEAST ONE SINGLE TURN LOCKING LAMINATION, THE LOCKING LAMINATION HAVING ENDS ABUTTING ONE ANOTHER TO DEFINE A BUTT JOINT LOCATED ON A LEG OF THE CORE DIFFERENT FROM THE FIRST LEG. 